Various butyl rubber formulations have been molded into several forms of elastomeric sealing barriers such as stoppers, diaphragms and pistons for pharmaceutical containers including vials, cartridges, syringes and the like. Butyl rubber barriers are desirable in these applications due to their good elasticity, moldability, inertness and consequent non-reactivity when placed in prolonged contact with pharmaceuticals. Most, if not all, butyl rubber formulations, however, require a silicone lubricant coating to ensure ease of axial movement within rigid structures such as syringes, cartridges, or the like. Alternatively, silicone-based rubber compounds such as SILASTIC.RTM. (registered trademark of Dow Corning Corporation) can be employed to provide some degree of lubricity.
Regardless of whether silicone is used in the rubber compound or as a secondary lubricant, silicone can compromise the purity of many surrounding pharmaceuticals due to possible reaction with and/or contamination of the pharmaceuticals housed in the relevant container when stored for long periods of time. Therefore, rigid containers such as cartridges which use conventional silicone-based sealing barriers cannot be safely used for long term storage with many pharmaceuticals.
For this reason, coating processes for coating rubber with non-reactive materials such as polytetrafluoroethylene available as TEFLON.RTM. (registered trademark of Dupont Corp.) have been developed. TEFLON.RTM. coating is desirable due to its low friction surface and inertness, but presents fabrication problems for some structures.
With conventional technology, TEFLON.RTM. may not be applied to typical resilient sealing pistons or stoppers, due to their non-flat configuration and thermal expansion. Therefore, coating a conventional elastomeric sealing stopper with TEFLON.RTM. rather than silicone is not a practical alternative.